The Idrija Municipal Museum was officially established on 21 January 1953. Its first principal was Srečko Logar, and the museum was located in the former wheat granary – storehouse. In 1954 the museum was entrusted with the management of Idrija's Gewerkenegg Castle, where it is still domiciled today.
Milestones in the fifty-year operation of the Idrija Municipal Museum:
1952 – The Museum Committee takes charge of certain mine facilities (storehouse, Idrija kamšt (water wheel), Kley's pump, several machines and devices from the separation plant, smelting plant and the electric power plant)

1954 – The famous Idrija kamšt (mine's water pumping device powered by a wooden wheel with a diameter of 13.6 m) is displayed to the public

1956 – The first two exhibition rooms are arranged in the castle (geological-mineralogical collection, Pirnat's Room)

1957 – The museum takes charge of the Slovenia Partisan Printing Shop on Vojsko plateau

1963 – The museum assumes management of the Franja Partisan Hospital in Dolenji Novaki near Cerkno

1956 / 1968 – Enlargement of museum collections and setup of a new permanent exhibition: Karst-speleological collection, mine presentation, Smelting Department, Department of Rescue and Protective Equipment, National Liberation Struggle (NOB) Department, and the Art & History Department

1969 – Commencement of gallery activities, opening of the Idrija Gallery and organization of resounding art colonies

1972 – Divje Jezero (Wild Lake) is proclaimed the first museum in nature in Slovenia,

1978 –
Opening of NOB Department in the old school building in Cerkno,

1985 –
Purchase of miner's house at Bazoviška 4 in Idrija and takeover of Bevk's homestead in Zakojca

1988 –
Commencement of extensive renovation works on the castle building (interior, courtyard, facade)

1989 / 1990 –
Salvage of the Franja Partisan Hospital from beneath a massive rockfall

1990 –
Relocation of mine machines and devices from the castle courtyard to Francis' Shaft – Technical Department of the Museum, where their restoration is conducted; individual exhibition areas are gradually opened to visitors: machines (1992), devices (1998) and engines (2000)

1990 –
Opening of renovated Bevk's homestead in Zakojca on the 100th anniversary of the birth of writer France Bevk

1991 –
Completed restoration of all three klavže (stone water barriers used for floating timber) on the Idrijca and Belca rivers

1990 / 1994 –
Restoration works on the Idrija kamšt (water wheel)

1995 –
Opening of permanent exhibition, entitled Five Centuries of the Mercury Mine and the Town of Idrija on the first floor of the castle

1997 –
For the above-mentioned exhibition and its entire range of activities, the museum receives an award from the European Museum Forum and is declared Best European Museum of Industrial and Technical Heritage

1998 / 2001 –
Restoration of museum building in Cerkno and arrangement of rooms for new permanent exhibitions

2003 –
Opening of two permanent exhibitions: Milestones of the 20th Century at Gewerkenegg Castle in Idrija, and The Region of Cerkno Through the Centuries in the Cerkno Museum

2005 –
Completion of restoration works on the Kanomlja klavže (water barriers)

2006 –
Opening of permanent exhibition in the Cerkno Museum, entitled Pust is to Blame! – A Story about the Laufarji from Cerkno; conduction of extensive rehabilitation works on the slope of Veliki Njivč above the Pasica Gorge, enabling safe passage of visitors to the Franja Partisan Hospital.

2008 –
Opening of permanent exhibition, entitled Idrija Lace, A History Written in Thread

2010 –
Opening of the reconstructed Franja Partisan Hospital after a disastrous flood in September 2007.